How Rope Tension Mechanisms Work

The Simple Engineering Behind Precise Tensioning

Whether you are working to secure the rigging of a boat, tighten a garden fence, installing architectural cable railings, or installing theatrical equipment, the precise level of tension is vital. Not only will inadequate levels of tension cause the wire rope to droop and shift, but excessive levels of tension may cause damage to components and wires, subsequently creating dangerous assemblies.

The problem lies in the fact that perfect levels of tension are not easy to attain. Rope strand materials may stretch when under tension, and components will expand and contract when affected by temperature. Over time, things will shift. It is necessary to find a way to fine-tune the level of tensioning after fitting the wire rope assembly and to make adjustments as necessary over the life of the equipment.

Turnbuckles and Rigging Screws provide an easy and sophisticated solution to the complex process of tensioning. But how do these tension mechanisms really work?

The Threading Mechanism Explained

The principle behind Turnbuckles and Rigging Screws is the same.

The Threading Mechanism works as follows: The central body of the device has a series of internal threads at both ends.

The cleverness of this mechanism lies in the fact that one of the ends of the device has a right-hand thread, while the other end has a left-hand thread. When the central body of the device is rotated clockwise, both ends of the device screw into place. The end of the device with the right-hand thread screws into place in one direction, and the other end screws into place in the other direction.

If you turn anti-clockwise, both ends move outwards, hence lengthening the entire piece and relieving tension. Turning clockwise will bring the ends closer, thus tightening the assembly.

It is these two threads that make these end fittings extremely efficient. You are, in effect, adjusting two things at once with a simple rotation, as opposed to one thing with a simple thread.

How often you turn a thread will depend on the level of tension you need.

Open Body vs Closed Body End Fitting Designs

If you were to walk into any hardware store, you would find two vastly different end fitting styles for wire rope tensioning, although they both have exactly the same function.

The turnbuckle end fitting has an open frame-style end piece, whereby you can actually see the rods threading through the middle. It is lighter, cheaper, and works just as well as the other end fitting styles.

Rigging screws have a closed central piece, whereby you cannot actually see inside, just a solid middle piece with end pieces protruding out of both sides.

Both styles have exactly the same function, with no difference at all, although the closed style is much more polished and not as industrial, which might be required for architectural designs where the final look is important.

Basic Understanding of End Fitting Styles

The end components of these tensioners vary from one type to another to cater to different connection demands. For instance, the eye end fittings have closed loops, which make them suitable for permanent anchoring. The hook end fittings allow for easy connection because they can slide into an eye plate or onto chain. They are thus suitable for temporary anchoring. The jaw end fittings, also called fork end fittings, provide a compromise between the eye bolts and shackles and are relatively easy to use.

Some of them may be provided with different configurations, for example, having one end with an eye and the other end with a hook.

For a variety of tensioning solutions available with different end configurations, as well as material and specification offerings, it is recommended to compare both rigging screws and turnbuckles. Checking the material is suitable for the application to ensure safety and longevity for any tensioning application.